The invention relates to vehicle seats and particularly to aircraft seats. A critical aspect of survivable aircraft crashes has been the ability of the seats to remain attached to the floor structure. In certain accidents, the seat track in the floor of the aircraft has fractured when overloaded by forces applied to it by a seat. It is well known that a given seat design having a predetermined distance between its front and rear legs can be made to absorb more "G" loadng than the amount currently specified by the United States Federal Aviation Administration (FAA), which is noted supra. However, to do so, the seat tracks and other supports in the aircraft floor would probably have to be replaced with much stronger and heavier members. Furthermore, any modification of the basic airframe structure of existing aircraft would be extremely expensive. Also, the additional weight of stronger supports would cause a significant increase in the operating cost.
It is also known that increasing the spacing between the front and rear support fittings for the front and rear legs of a seat will reduce the bending load exerted on the seat track in a crash situation. This is because the load applied to the rear fitting tends to lift the seat track while the load applied to the front fitting tends to depress the track. Typically, a seat is designed to fail by having its front legs collapse in a controlled mode after the design load is reached. Additional loading generally causes the rear track fittings to tear out of the seat track or causes the seat track to tear out of the floor. As increased operating costs have forced carriers to reduce the pitch distance between seats from about 34 inches (86.4 cm) to as little as 28 or 29 inches (71-74 cm) to accommodate more passengers, it has become quite desirable to minimize the front to rear leg spacing in order to preserve as much passenger foot and leg access room behind the seat as possible. However, as previously noted, the strength of existing seat tracks places a distinct limit on how closely the legs can be spaced for a given seat and seat frame configuration. Under current FAA regulations, using an NAS 809 dummy block (National Aircraft Standard promulgated by the Aircraft Industries Association of America, Inc.), a seat must be able to withstand, in a static test, a force of 6 "G's" with no permanent deformation. The seat can yield, but must not fail, when subjected to loads of 6-9 "G's". The desired failure mode is to have the front legs start to collapse at 9 "G's" so that the rear studs will not pull out of the track, or lift the track from the floor supports, at loads of less than 12 "G's". To permit a particular existing seat, which has a 16 inch (40.6 cm) leg spacing, to resist failure at higher loads, for example, at 16 "G's" rather than 9 "G's", without altering the seat track or aircraft, the leg spacing must typically be increased to about 19 inches (48.3 cm). However, such 19 inch (48.3 cm) spacing is quite undesirable since it greatly reduces passenger access room behind the seat.
It is further known that seats can be manufactured with portions thereof adapted to absorb energy so as to decrease the "G" forces applied to a seat and its occupant in the rapid deceleration conditions of a crash landing. For example, Brewster U.S. Pat. No. 2,959,207 discloses a telescoping rear leg which includes a cylindrical tube which absorbs energy when it is reduced in diameter by being drawn over a die. A somewhat similar arrangement for a front leg is disclosed in Spielman U.S. Pat. No. 3,059,966.